A steel part or component constituting machinery includes many friction portions and thus is demanded in many cases to have abrasion resistance. A technique of carburizing the surface of a steel part or component to improve abrasion resistance is also used for parts or components constituting a vehicle. Actually, the parts subjected to the carburizing treatment are used throughout a vehicle.
Carburizing an entire part can enhance the surface hardness of the part but may cause problems in which machining is difficult, breakages or cracks are apt to occur during welding, and others. Therefore, there is a demand to partially carburize only a desired portion. Various studies have accordingly been made to obtain a part in which a non-carburizing portion needing no carburizing is not carburized.
Patent Document 1 discloses a technique of suppressing and preventing carburizing and metal dusting. The surface of a metal member to be exposed to high-temperature carbon gas is plastic-deformed or plastic-strained in advance. This can control a carburizing depth in the carburizing treatment. This makes it possible to restrain a phenomenon in which metals and alloys disintegrate or decompose into dust in a carburizing atmosphere called metal dusting and the dust is blown off by a gas flow or the like, forming pits or causing abrasion wastage.
Patent Document 2 discloses a technique of preventing carburizing of a welded portion. Considering circumstances that carburizing occurs in a welded joint, a first layer is welded to a base material and then a silicon-containing material is coated or stacked to a back side of the base material. This is reacted or fused (melted) by use of welding heat for second and subsequent layers, thus forming an oxide coat made of silica dioxide. This method can form the oxide coat, thereby preventing carburizing of the welded portion.
Patent Document 3 discloses a technique of a carburizing inhibiting material. A copper alloy coat is formed in a portion in which a screw part is to be formed. Thereby, the carburizing of the relevant portion is prevented during subsequent carburizing of a part.
Patent Document 4 discloses a technique of preventing carburizing in a carburizing treatment. A tin coat is formed as a mask member on a portion desired to avoid carburizing, thereby preventing carburizing of the relevant portion.
Patent Document 5 discloses a technique of preventing carburizing. On a portion desired to avoid carburizing, two or more kinds of carburizing inhibiting agents containing a first substance and a second substance is applied. The first substance is a substance, such as boric acid and boron oxide, that can be sequentially melted in a temperature range from a first temperature to a treating temperature, thereby sequentially coating the metal surface. The second substance is a substance, such as a mixture of rubber and an adhesive material, that can be melted in a temperature range from a normal temperature to at least the first temperature, thereby coating the metal surface. By such application of the carburizing preventing agent during a carburizing treatment, it is possible to prevent the carburizing treatment.